Cerium based abrasives are used not only in traditional polishing of optical glass but also for polishing glass for liquid crystal display and hard recording medium. It is required that this type of abrasives has high polishing rate and produces a polished surface with excellent quality.
Generally, cerium based polishing powders are manufactured by following methods: rare earth (comprising cerium and optionally lanthanum, and optionally further rare earths) carbonates are slurried, wet pulverized, and treated with mineral acid such as HF. The obtained slurry is filtered, dried, and roasted, followed by subsequent pulverization and classification to obtain desired particle size. This process has the disadvantage of unable to adjust the composition of the abrasive materials, and therefore the polishing rate and the quality of polished surface cannot be improved greatly.
WO2007/052555A1 discloses a cerium polishing agent wherein the cerium oxide content relative to the total rare earth oxide (TREO) is no less than 90% by mass. This cerium polishing agent is characterized in that at least one specific element selected from the group consisting of Ti and group 5-12 elements having an atomic number of 80 or less is contained in an amount of 0.001-2.0% by mass relative to the total mass of the polishing rate.
EP1707534A1 describes an oxide solid solution powder composed mainly of an oxide of cerium that can be used as an abrasive. When glass materials such as glass substrates are polished by using the oxide solid solution powder in which an oxide of calcium is dissolved as a solid solution in rare earth oxides composed mainly of cerium oxide, the oxide solid solution powder can provide polished surfaces having a high polished surface precision, and is suitable for abrasives.
JP2007-9214A discloses a cerium-based abrasive which is free of F, and works at a high abrasion speed and with a good abrasion precision. The resulted abrasive has an F content of 0.5 wt % or less, and an alkali metal or alkaline earth metal content or an alkali metal and alkaline earth metal total content of 0.3-5 wt % in terms of elements.
In order to meet the required high polishing rate and excellent surface quality, some transition metal elements and alkaline earth metal elements such as Ti, Zr, and Ca were used in abrasives. However, it was required to have cerium content higher than 90% to obtain high polishing rate. In some cases, two or more of the elements were required in order to obtain a solid solution and to have both high polishing rate and high polished surface quality at the same time.